CVE-2023-52854

About vulnerability

In the Linux kernel, the following vulnerability has been resolved:

padata: Fix refcnt handling in padata_free_shell()

In a high-load arm64 environment, the pcrypt_aead01 test in LTP can lead to system UAF (Use-After-Free) issues. Due to the lengthy analysis of the pcrypt_aead01 function call, I’ll describe the problem scenario using a simplified model:

Suppose there’s a user of padata named user_function that adheres to the padata requirement of calling padata_free_shell after serial() has been invoked, as demonstrated in the following code:

struct request {
struct padata_priv padata;
struct completion *done;
};

void parallel(struct padata_priv *padata) {
do_something();
}

void serial(struct padata_priv *padata) {
struct request *request = container_of(padata,
struct request,
padata);
complete(request->done);
}

void user_function() {
DECLARE_COMPLETION(done)
padata->parallel = parallel;
padata->serial = serial;
padata_do_parallel();
wait_for_completion(&done);
padata_free_shell();
}

In the corresponding padata.c file, there’s the following code:

static void padata_serial_worker(struct work_struct *serial_work) {
...
cnt = 0;

while (!list_empty(&local_list)) {
...
padata->serial(padata);
cnt++;
}

local_bh_enable();

if (refcount_sub_and_test(cnt, &pd->refcnt))
padata_free_pd(pd);
}

Because of the high system load and the accumulation of unexecuted softirq at this moment, local_bh_enable() in padata takes longer to execute than usual. Subsequently, when accessing pd->refcnt, pd has already been released by padata_free_shell(), resulting in a UAF issue with pd->refcnt.

The fix is straightforward: add refcount_dec_and_test before calling padata_free_pd in padata_free_shell.

Affected product:

AlmaLinux 9.2 ESU , CentOS 7 ELS , Oracle Linux 7 ELS , RHEL 7 ELS , Ubuntu 16.04 ELS , Ubuntu 18.04 ELS , Ubuntu 20.04 ELS

Affected packages:

kernel @ 3.10.0 (+7 more)

In the Linux kernel, the following vulnerability has been resolved:

padata: Fix refcnt handling in padata_free_shell()

In a high-load arm64 environment, the pcrypt_aead01 test in LTP can lead to system UAF (Use-After-Free) issues. Due to the lengthy analysis of the pcrypt_aead01 function call, I’ll describe the problem scenario using a simplified model:

Suppose there’s a user of padata named user_function that adheres to the padata requirement of calling padata_free_shell after serial() has been invoked, as demonstrated in the following code:

struct request {
struct padata_priv padata;
struct completion *done;
};

void parallel(struct padata_priv *padata) {
do_something();
}

void serial(struct padata_priv *padata) {
struct request *request = container_of(padata,
struct request,
padata);
complete(request->done);
}

void user_function() {
DECLARE_COMPLETION(done)
padata->parallel = parallel;
padata->serial = serial;
padata_do_parallel();
wait_for_completion(&done);
padata_free_shell();
}

In the corresponding padata.c file, there’s the following code:

static void padata_serial_worker(struct work_struct *serial_work) {
...
cnt = 0;

while (!list_empty(&local_list)) {
...
padata->serial(padata);
cnt++;
}

local_bh_enable();

if (refcount_sub_and_test(cnt, &pd->refcnt))
padata_free_pd(pd);
}

Because of the high system load and the accumulation of unexecuted softirq at this moment, local_bh_enable() in padata takes longer to execute than usual. Subsequently, when accessing pd->refcnt, pd has already been released by padata_free_shell(), resulting in a UAF issue with pd->refcnt.

The fix is straightforward: add refcount_dec_and_test before calling padata_free_pd in padata_free_shell.